This invention relates to a method and apparatus for the sputtering of coatings from a cathodic magnetron sputtering device upon temperature-sensitive substrates such as plastic ophthalmic lenses.
Plastic ophthalmic lenses such as eyeglass lenses have become popular in recent years, due particularly to their light weight. Coatings commonly are applied to the lenses for any of a number of reasons. Antireflective coatings, for example, reduce the reflected light from the lens surfaces. Other coatings increase the hardness and scratch resistance of plastic lens surfaces. Yet other coatings are used to provide small amounts of color to the lenses, either for cosmetic purposes or to reduce the incidence of radiation of particular wavelengths, e.g., UV light.
Ophthalmic lenses commonly are made from lens blanks, and coatings are applied to the lens blanks by applying a coating liquid to the lens blanks as by spraying, dipping, etc. Depending on the coating desired, the coating process may require a series of sequential steps, followed by drying, irradiating with light to cross-link polymers in the coating, etc. As a result, the coating process is relatively slow, and great care must be taken to preserve the desired characteristics of the coating solutions. Antireflective coatings, consisting typically of a series of metal oxide layers having alternating high and low indices of refraction, commonly are applied to lens blanks by batch-processing vacuum deposition techniques in which the temperature of the lens blanks can be controlled.
Magnetron sputtering techniques have been used for applying coatings to temperature-resistant substrates such as glass. In ordinary magnetron sputtering techniques, a temperature-resistant substrate to be coated is exposed to a magnetron sputtering target in a high vacuum environment, and molecules of the target material are ejected from the target to impinge upon and coat the substrate. The loss of electrons to the substrate also causes the temperature of the substrate to rise. When temperature-sensitive materials such as polymers are attempted to be coated in this manner, the impingement of electrons on the polymer rapidly heats the substrate. The heat capacity of polymers commonly is substantially less than that of glass. Moreover, plasma temperatures can rise substantially. As a result, magnetron sputtering of coatings onto the surfaces of temperature-sensitive materials such as polymer lens blanks has not gained favor because of the tendency of such materials to soften and deform at elevated temperatures.
It would be desirable to provide a magnetron sputtering apparatus that would enable temperature-sensitive materials such as polymer lens blanks to be successfully coated without being unduly heated.
I have found that substrate heating in magnetron sputtering devices occurs primarily through the impingement of primary electrons on the substrate, that is, electrons that generally are not trapped in the magnetic field. Moreover, I have found that electron impingement on the substrate can be largely avoided by placing a cooling anode within the sputtering chamber in a position close enough to the cathode target to capture primary electrons not captured in the magnetic field and that otherwise would impinge upon the substrate, but yet oriented, with respect to the cathode, in a field noninterfering position; that is, in a position that does not cause interference with magnetic flux lines and thus produces no significant effect upon sputtering erosion patterns in the target or sputtering uniformity.
Thus, my invention in one embodiment provides an apparatus for the cathodic magnetron sputtering of a temperature-sensitive substrate. The apparatus comprises a vacuum chamber having a work supporting station and a magnetron sputtering target in sputtering opposition to the work supporting station. The apparatus produces a magnetic field serving to contain, in an oval pattern, a gas plasma cloud to eject target material toward the work supporting station.
The apparatus includes an anode that is carried between the target and the work supporting station sufficiently out of said magnetic field so as to produce no significant effect upon the magnetic field or sputtering erosion patterns but yet sufficiently near the target as to collect electrons not captured by the magnetic field and that otherwise would impinge upon and heat a substrate supported by the work supporting station. In a preferred embodiment, the anode is externally fluid-cooled preferably by an external source of liquid coolant that is supplied to the anode during the coating operation.
In another embodiment, my invention provides a method for cathodic magnetron sputtering of target material on the surface of heat-sensitive substrates in a magnetron sputtering apparatus that includes a vacuum chamber having a work-supporting station and a magnetron sputtering target in sputtering opposition to said work supporting station. The apparatus produces a magnetic field serving to contain, in an oval pattern, a gas plasma cloud to eject target material toward the work-supporting station. The method comprises the steps of:
a. providing within the vacuum chamber an anode carried adjacent but out of the oval pattern,
b. positioning the anode sufficiently out of the magnetic field so as to have no significant effect upon the magnetic field nor the uniformity of the deposition process, but in position with respect to the target as to collect electrons not captured by the magnetic field and that otherwise would impinge upon and heat a substrate supported by the work supporting station, and
c. withdrawing energy from the anode.
Preferably, the anode is carried generally centrally (but out of) the oval pattern, although the anode can also be carried to the side of the oval pattern. Energy may be withdrawn from the anode by means of external fluid cooling and/or by conduction of electrons away from the anode, as well as by radiation.